Friday, March 13, 2015

Three Parent In Vitro Fertilization

January 27, 2015 marks the date
that a formal request was submitted to the FDA to assemble a committee to seek
approval for clinical trials; testing egg and zygote modification within in
vitro fertilization. The goal of this specific technique is to eradicate the
transmission of specific mitochondrial diseases between the mother and child.

Mitochondria are a specific type of
organelle found within human cells responsible for creating the vast majority
of the energy with separate genome from the genetic material present within the
nucleus. Mutations within mitochondrial DNA can cause a variety of
mitochondrial diseases, many of which remain unknown and uncharacterized due to
the fact that they cause a variety of symptoms, which differ on a case-to-case
basis. These defects arise when inherited from past generations or from
spontaneous mutations in both mitochondrial and nuclear DNA. Mitochondrial
diseases most often affect the organs with a high metabolic demand such as the
heart, brain, and liver. For this reason, those that have a mitochondrial
genome defect often undergo multi organ failure and eventually die. There is
currently no living cure for these genetic defects and the resulting conditions
that ensue from them.

Three-parent
in vitro fertilization is a technique that was developed as a solution to
mitochondrial disease by performing a “mitochondrial replacement.” Two major
techniques have been developed in order to solve this problem, each of which
would lessen the amount of mitochondrial diseases that occur from
parent-offspring transfer and mutations within the mitochondrial DNA.
Mitochondrial disease resulting from nuclear DNA defects and those from spontaneous
mutations within a person’s lifetime will remain cureless.

The first
technique was given the name pronuclear transfer. Within this method the
intended, mutated mother’s egg and donor’s egg are fertilized with sperm in
vitro. Before the sperm and ovum fuse they both contain pronuclei. After one
day, when the fertilized eggs are still single-celled organisms, the pronuclei
are removed from zygotes. The pronuclei from the donor egg and sperm are
discarded and replaced with the pronuclei from the intended, mutated mothers
egg and sperm. The resulting embryo will grow and develop, eventually being
placed back into the mother to undergo typical in vitro fertilization
processes. The mutated mitochondrial DNA from the intended mother is discarded
and majority of her genome is transfer to her offspring through the nuclear
transfer. The resulting zygote contains nuclear DNA from the intended mother
and healthy mitochondria and cytoplasm from the donor egg. Though the transfer
has been successfully carried out in mice, when attempted on human zygotes, many
attempts have resulted in abnormal fertilizations.

From Center for Genetics and Society

http://www.geneticsandsociety.org/article.php?id=6527

The second
technique being investigated; called spindle transfer, is similar to the
pronuclear transfer, though a zygote is not formed until later in the process.
The nucleus is removed from the oocyte with a mutated form of mitochondrial
DNA. The nucleus is then placed into an enucleated donor oocyte, in which the
healthy mitochondria remain in the cytoplasm. Sperm will then fertilize the
reconstructed oocyte and the zygote will be implanted within the intended
mother to undergo a typical in vitro fertilization process. The transfer has
successfully been complete on primates resulting in less then 1% of
mitochondrial DNA transfer to the healthy oocyte.

From Center for Genetics and Society

http://www.geneticsandsociety.org/article.php?id=6527

The United
Kingdom has recently approved the procedure to be available within fertility
clinics starting at October 29, 2015, while the United States has begun
assembling a committee to review the techniques and determine whether human
clinical trials will proceed. Mitochondrial replacement techniques are
currently surrounded by countless ethical and medical debates throughout the
nation.

This technique
has not been studied long-term in humans. The method of mitochondrial
replacement is one of the first implemented that will modify the human germline
and the affect on subsequent generations is a still a complete mystery to
scientists. Human embryonic modification also walks the “slippery slope” of
where science can and should be involved in people’s lives. The nature vs.
nurture debate arises when some people choice to believe that science should
not be involved in processes that in the fast have been left up to ‘fate.’ The
altering of embryos ultimately affects the future of the resulting child. Embryonic
modification completely takes away any informed consent due to the fact that
the child has no say and the parents are not fully informed with the limited
knowledge of the techniques.

Three-parent
in vitro fertilization is an entirely new technique that is becoming available
for people who have been diagnosed with specific mitochondrial mutations in
order to not transmit them to their future offspring. Though this technique is
not applicable to a large portion of the population, with progress on embryonic
modification and gene transfer techniques scientists may be able to eradicate
the transfer of multiple diseases.

6 comments:

This is a very interesting topic because it opens the door of germline modification. Where should we draw the line for changing the human germline because with CRISPR we now process an easy method for unhindered use. However, the implication could be profound on the future of humanity. Even if we were to limit the use in developed countries, undeveloped nations with lax regulations could produce clinics to modify the germline for a price. I wonder if taking this small step for mitochondrial disease is the begging of the next era in human evolution.

I agree with Phillip. I think that the intentions of this particular therapy are good, but I fear that researchers will keep pushing its use further. After mitochondrial replacement, it will be used for various other genetic diseases, and ultimately people will be using germline modification to select the hair and eye color of their child. I know that it is a slippery slope, but I think there is some reality in it.

I think the bioethical issues that you briefly mentioned at the end of you post offer interesting perspectives that should be analyzed. Many people, when they hear that a child can be brought into this world by three parents, may be apprehensive with this type of in vitro fertilization. However, it is important to realize that the "third" parent is really only contributing mitochondrial DNA, which doesn't radically change any features of the child besides eradicating disease. It is very different from the use of in vitro fertilization to create "designer babies," which many people are concerned about. For this technology, education is critical for the general public.

Despite any potential ethical problems with this procedure, it is extremely clever. I love the idea and I'm glad that it's been so successful. This wasn't addressed in much detail, but will there be much demand for this? I would imagine that egg cells are not easy to come by, and would probably be expensive, especially if there must be much testing on the egg cells before the donor can donate them. As for the bioethical issues of altering the genes of the embryo, it is strange that preventing disease is seen as a bad thing. This is a completely painless treatment for the embryo which will likely drastically improve the life of the person. Also, the slippery slope argument can only be taken so far; it is logically fallacious to say that, just because we are preventing disease with gene modification today, we will be engineering our children to be smart and good-looking tomorrow. This slippery slope is something to be concerned about, but as a society we might not slip down this metaphorical slope.

This has the potential to be a very useful technique, especially because people who are at risk to pass along mitochondrial diseases may be weary about having kids the "old-fashioned" way. I agree with Hannah, with any of these types of techniques there comes a time when we have to decide where to draw the line. How much zygote modification (even if it is solely for the purpose of disease prevention) is too much? There is an obvious ethical question here about if this type of modification is the right thing to do, to which there is no answer. Sarah mentioned that this is very different from using technology to create designer babies, but is it? The general idea is the same - specific modification of a zygote. I understand why people would be interested in using techniques like this, but I also understand arguments against is. If this type of thing is allowed in the future, I think it's going to be hard to tell people that they shouldn't or can't select their baby's eye or hair color. This is a very interesting yet complicated subject.

I think a lot of science and technology could be used in the wrong ways and the argument of a slippery slope is a concern anywhere, but often the benefits outweigh the risks. I feel that in this case they definitely do. Allowing parents who can't have children or cannot have healthy children to have their own healthy children is incredible. I think these techniques have a lot of promise and I do not think research should be stopped just because the mechanisms behind the therapy could be used immorally.